The Computational and Biological Vision Group, led by Hüseyin Boyacı and Katja Doerschner is part of Aysel Sabuncu Brain Research Center and National Magnetic Resonance Research Center (UMRAM), and operates jointly with the Department of Psychology and the Neuroscience Graduate Program, Bilkent University. Research in the lab is focused on visual perception and its neuronal underpinnings. We use behavioral experimentation, neuroimaging (fMRI), and computational modeling to find answers to problems of vision science.

Here you can find out more about our projects.

Follow us on Twitter

Recent News
Graduate School Open House

Bilkent Univesity Graduate School of Science & Engineering is organizing a virtual open house on the 27th of March (2021). Neuroscience Program will be there. For more details see http://gradopenhouse.bilkent.edu.tr/

New Preprint

Urgen, Boyaci, A recurrent cortical model can parsimoniously explain the effect of expectations on sensory processes

A schematic illustration of the cortical model. The model has one input, one decision and three intermediate layers, and three category-specific feature units for house (H), face (F) and scrambled (S) images. Weights of the connections are depicted by the thickness of the arrows. Priors, Ŷ i, are initialized in the beginning of the trial based on the cue and its validity. Later they are updated with past values of layer 3 unit responses. All unit responses are updated until the end of the presentation. Number of iterations in a trial is determined by the stimulus presentation duration, τ, divided by Δt, where Δt defines how long each iteration lasts in the system. A final decision is made by the model based on the sum of layer 3 house and face unit responses on the left and right side of the visual field.

The manuscript shows that a simple and parsimonious cortical model can explain behavioral effects of prediction. The model does not require separate “error” and “representation” units as posited by leading models of predictive processes in the brain. The model also provides a unifying framework for behavioral and neuronal data.

New Projects

We have a new project supported by TUBITAK. The project is titled “Center-surround interaction in motion perception”. In this project we will investigate the details of center-surround interaction in motion perception, including the role of spatial attention.

In another project led by Ozgur Mustecaplioglu (principal investigator) from Koc University, we will collaborate on quantum metrology using the human eye. The project is titled “Applications of Quantum Metrology with Human Eye”, and supported by TUBITAK.

New STAR Member

Asli Tekin, an undergraduate research assistant in CBVG, received a STAR fellowship from TUBITAK. She will work in the project “Neuronal Basis of Perceptual Learning”, which is supported by TUBITAK. Congratulations Asli!

Buse Merve Ürgen successfully defended her Ph.D. thesis!

Buse defended her thesis entitled “Behavioral and Computational Investigation of the Effect of Prior Knowledge on Visual Perception” on January 14, 2021. Please follow this link to see the abstract. We wish her the best of luck in her career!

New Publication

Schmid, Boyaci, & Doerschner, “Dynamic dot displays reveal material motion network in the human brain”

Using dynamic dot displays, we show that a large network of brain regions respond to material motion. The dynamic dot displays are similar to those in biological motion studies, and they allow researchers to isolate motion cues from all other cues to material properties (e.g. surface reflectance). Interestingly, the areas that are found to respond to material motion in this study constitute a superset of those found to respond to biological motion in previous studies.

New Publication

Urgen, Boyaci, “Unmet expectations delay sensory processes“

Prior knowledge and expectations play a substantial role in recognition and decision-making processes by governing the interpretation of the sensory stimulus and allowing us to make fast and accurate decisions. Whether and how early sensory processes are affected by expectations, however, has remained a controversial issue. Using a behavioral experiment and a recursive Bayesian model, Urgen & Boyaci (2021) investigated the effect of expectations on perceptual thresholds and unveiled the possible mechanisms that underlie the observed effects. Specifically, they showed that unlike what is suggested for higher-level mechanisms, valid expectations do not facilitate perceptual processes, instead, unmet expectations delay them. Their modeling findings revealed that the mechanism that underlies this delay is the need for further processing required by the system to complete the sensory process. Urgen & Boyaci (2021) also discussed possible neural mechanisms that can explain their findings within the predictive processing framework.

Dilara Erişen successfully defended her Master’s thesis!

Dilara defended her thesis entitled “Investigating the effects of perceptual learning on the function and microstructure of the visual cortex” on December 3, 2020. We wish her the best of luck for her PhD!

New Publication

Altan, Boyaci, “Size aftereffect is non-local”

Prolonged exposure to a certain size stimulus alters the perceived size of a subsequently presented stimulus at the same location. How the rest of the visual space is affected by this size adaptation, however, has not been systematically studied before. In this study, we tested size adaptation at the adapter location as well as the rest of the visual space. Our results showed that the perceived sizes of target stimuli were affected by the adapter, not only at the adapter location but also at other locations. These findings demonstrate that size adaptation causes widespread distortion of the visual space and alters perceived size. We discuss possible computational models that may underpin the perceptual effect in the article.

New Publication

Er, Pamir, Boyaci,  “Distinct patterns of surround modulation in V1 and hMT+”, https://doi.org/10.1016/j.neuroimage.2020.117084

Using fMRI and a well-studied motion paradigm, in which sensitivity to direction of motion increases (decreases) for a low (high) contrast stimulus as its size gets bigger, Er et al. show that patterns of center-surround interaction are different in primary visual cortex (V1) and middle temporal complex (hMT+). Furthermore, we show that the divisive normalization model can successfully predict the responses in V1 and hMT+, and link the behavioral and fMRI data.

Recent preprints from CBVG!

CBVG has recently shared four preprints:

Beyza Akkoyunlu successfully defended her Master’s thesis!

Beyza defended her thesis entitled “Functional changes in the human cortex over the course of visual perceptual learning” on March 20, 2020 at Aysel Sabuncu Brain Research Center. Please follow this link to see the abstract. We wish her good luck in her career!

Seminar: “Oscillatory Recurrent Gated Neural Integrator Circuits (ORGaNICs): A Unifying Theoretical Framework for Neural Dynamics” by David Heeger @ Bilkent!

davidheegertalk

Prof. Heeger recently gave a talk entitled “Oscillatory Recurrent Gated Neural Integrator Circuits (ORGaNICs): A Unifying Theoretical Framework for Neural Dynamics” at Bilkent as part of Neuroscience Seminar Series Fall 2019. Later, he gave another talk on his recent model at Dynamics in Vision and Touch (DyViTo) workshop held in Cappadocia, Turkey. 

Please click here to see the talk announcement.

Six Master’s theses defended successfully!
20190704_102138

Batuhan Erkat: Mapping Human Visual Cortex With Population Receptive Field Model: Tuning FMRI and Stimulus Parameters, and Exploring Receptive Field Sizes

Cemre Yilmaz: Effect of Visual Stimuli With Fearful Emotional Cue on Population Receptive Field Estimates

Ecem Altan: The Spatial Extent of Size Adaptation Effect in Peripheral Vision

Ilayda Nazli: The Effect of Orientation-Related Prior Probability Information on Contrast Perception

Cem Benar: Temporal and Spatial Nonlinearities in fMRI BOLD Response in Human Primary Visual Cortex

Hossein Mehrzadfar: Comparing the Performance of Humans and 3D-Convolutional Neural Networks in Material Perception Using Dynamic Cues

Congratulations Cemre, Batuhan, Ecem, Ilayda, Cem and Hossein for the fantastic job!

Save the dates! Six Master’s thesis dissertations in the first week of July, 2019

July 1: Cemre Yilmaz, Batuhan Erkat, Ecem Altan

July 2: Ilayda Nazli

July 4: Cem Benar, Hossein Mehrzadfar

Görkem Er successfully defended his Master’s thesis!

Gorkem defended his thesis entitled “The Role of Contrast and Size in Motion Perception: Behavioral and Neuroimaging Study of Center-Surround Interactions in Primary Visual Cortex (V1) and Middle Temporal Area (MT+) ” on September 13, 2018 at Aysel Sabuncu Brain Research Center. Please follow this link to see the abstract. We wish him good luck in his career!

Zahide Pamir successfully defended her PhD thesis!

webiste_phd_zahide

Zahide defended her PhD thesis entitled “The Effect of Context-dependent Lightness on Contrast Detection and Identification, and Its Neural Correlates” on 19 October, 2017 at Aysel Sabuncu Brain Research Center. Please click here for the abstract. We wish her all the best and success in her future career!

CBVG was at ECVP 2017!

ecvp2017

We as CBVG presented our work at ECVP 2017, Berlin. Please visit: http://vision.bilkent.edu.tr/publications/ for more information about our abstracts.